Principal Research seeks to increase the number and availability of evidence-based interventions applicable to elderly persons at high risk for depression and its complications, to those with difficult to treat mood disorders seen within the specialty mental health sector, and to those seen in the primary care sector, in rehabilitation centers, and in nursing home and other long term care settings. Intervention studies will address the following themes: (1) preventing depression and suicide in elderly persons at high risk; and improving, preventing, or delaying cognitive and functional impairments in elderly with depression; (2) improving treatment for difficult to treat mood disorders in later life (e.g., bipolar disorders, psychotic depression, and unipolar major depression responding only partially to first line treatment); and (3) identifying and removing barriers to effective depression treatment in community clinical settings. Cutting across these themes is the Center objective (4) of using infrastructure support to enhance research-training opportunities in mental health and aging and in community-based participatory research. These themes capture our movement from efficacy to effectiveness research, to services, dissemination, and practice research, as mandated in the NIMH Council report, Bridqin.q Science and Service. To this end the bidirectional linkages between the Principal Research Core and the Research Network Development Core are of critical scientific importance.